| Popis: |
The Blended Wing Body (BWB) aircraft offers a number of aerodynamic perfor- mance advantages when compared with conventional configurations. However, while operating at low airspeeds with nominal static margins, the controls on the BWB aircraft begin to saturate and the dynamic performance gets sluggish. Augmenta- tion of aerodynamic controls with the propulsion system is therefore considered in this research. Two aspects were of interest, namely thrust vectoring (TVC) and flap blowing. An aerodynamic model for the BWB aircraft with blown flap effects was formulated using empirical and vortex lattice methods and then integrated with a three spool Trent 500 turbofan engine model. The objectives were to estimate the effect of vectored thrust and engine bleed on its performance and to ascertain the corresponding gains in aerodynamic control effectiveness. To enhance control effectiveness, both internally and external blown flaps were sim- ulated. For a full span internally blown flap (IBF) arrangement using IPC flow, the amount of bleed mass flow and consequently the achievable blowing coefficients are limited. For IBF, the pitch control effectiveness was shown to increase by 18% at low airspeeds. The associated detoriation in engine performance due to compressor bleed could be avoided either by bleeding the compressor at an earlier station along its ax- ial length or matching the engine for permanent bleed extraction. For an externally blown flap (EBF) arrangement using bypass air, high blowing coefficients are shown to be achieved at 100% Fan RPM. This results in a 44% increase in pitch control authority at landing and take-off speeds. The main benefit occurs at take-off, where both TVC and flap blowing help in achieving early pitch rotation, reducing take-off field lengths and lift-off speeds considerably. With central flap blowing and a lim- ited TVC of 10◦, the lift-off range reduces by 48% and lift-off velocity by almost 26%. For the lateral-directional axis it was shown that both aileron and rudder control powers can be almost doubled at a blowing coefficient of Cu = 0.2. Increased roll authority greatly helps in achieving better roll response at low speeds, whereas the increased rudder power helps in maintaining flight path in presence of asymmetric thrust or engine failure, otherwise not possible using the conventional winglet rudder. |
